1. Integrated 2-D and 3-D Structural, Thermal, Rheological and Isostatic Modelling of Lithosphere Deformation: Application to Deep Intra- Continental Basins Stuart Egan

2. F Introduction: Modelling lithosphere extension and basin formation - basic concepts and initial models Modelling lithosphere extension and basin formation - basic concepts and initial models Importance of geological and geophysical data in model development Importance of geological and geophysical data in model development F Processes and modelling theory: Structural processes Structural processes Thermal effects - perturbation and re-equilibration Thermal effects - perturbation and re-equilibration Isostasy Isostasy Surface processes and the development of basin stratigraphy Surface processes and the development of basin stratigraphy F Case studies: Eastern Black Sea Eastern Black Sea South Caspian basin South Caspian basin Contents

3. Pure Shear (stretching) The McKenzie Model (Uniform Lithosphere Extension) The McKenzie Model (Uniform Lithosphere Extension) (McKenzie, 1978) The model quantifies subsidence occurring due to crustal thinning and uplift caused by the raising of hotter material at depth nearer to the surface, along with the associated Airy isostatic compensation The second half of McKenzie's model simulates the thermal subsidence phase of basin evolution

4. Subsidence curve generated by McKenzie model

5. BIRPS* Seismic Data Lewis basin Outer Isles Fault Orkney basin *British Institutions Reflection Profiling Syndicate

6. Integrated Model - parameters

7. Integrated Model - extension Chevron (Vertical Shear) Construction Temperature field perturbations Flexural Isostasy

8. Integrated Model of Lithosphere Extension Basins are generated by extension along a sequence of closely spaced faults, which flatten within the crust. Pure shear/stretching is assumed to deform the lithosphere below the faults and is distributed regionally. The large subsidence within the basin is partly attributable to the effects of sediment infill and isostatic loading. The Footwall and Moho are raised beneath the basin mostly as an isostatic response to crustal thinning. The stratigraphy in the basin shows post-rift thermal subsidence overlying syn-rift megasequences.

9. Integrated Model - shortening

10. Black Sea Location

11. Black Sea Tectonics

14. Uniform lithosphere extension

15. …..followed by shortening at margins

16. Crustal thickness can be used to define a Beta (“stretching”) profile

17. Uniform lithosphere extension based upon magnitude of crustal thinning

18. Depth dependent stretching - enhanced extension of lower crust and mantle lithosphere

19. Lithosphere strength distribution and inferred depth of necking/detachment “Cool” Lithosphere: “Warm” Lithosphere: Adapted from Braun and Beaumont, 1989

23. Brunet, et al, 2003 South Caspian Basin MIDDLE EAST BASIN EVOLUTION PROGRAMME

24. Confidential Data

25. SW-NE Cross-Section Part 1: Part 2: Sections produced from interpretation of seismic data by BP geoscientists. Note depth is in TWT There is an overlap and slight offset where sections intersect (see next slide) Confidential Data

26. Fault Deformation – Model input parameters Fault heave values are very approximate as they are difficult to estimate from data. However, extension due to faulting is very low Also, difficult to quantify the compressional deformation, which intensifies to NE.

27. Uniform Lithosphere Extension (based upon fault heave values) Subsidence in the basin is far too low. B max = 1.11! Time = 150Ma T e = 5 – 10 km  i = 2500 kg.m -3  c = 2850 kg.m -3

28. ….followed by compression Subsidence in the basin is still far too low.

29. Estimation of Moho Depth Moho depth based upon limited information (e.g. Mangino & Priestley 1998).  max = 3.5 Confidential Data

30. Reconciliation of fault-controlled extension and attenuation of the crust Enhances syn-rift subsidence due to thinning of the lower crust. Enhances syn-rift subsidence due to thinning of the lower crust. Enhances post-rift subsidence through increased initial heating of the lithosphere (Bmax = 3.5). Enhances post-rift subsidence through increased initial heating of the lithosphere (Bmax = 3.5). Overall subsidence is comparable to data. However, NE of section clearly not deep enough (more data required!). Overall subsidence is comparable to data. However, NE of section clearly not deep enough (more data required!). SWNE Crust Post-rift Syn-rift Subsidence due to compression Extensional and compressional faulting

31. Summary The first numerical models of lithosphere extension were developed about 25 years ago. These models were successful in showing how crustal attenuation, thermal perturbations and local isostatic compensation control basin subsidence and the evolution of syn- and post-rift stratigraphic sequences. The first numerical models of lithosphere extension were developed about 25 years ago. These models were successful in showing how crustal attenuation, thermal perturbations and local isostatic compensation control basin subsidence and the evolution of syn- and post-rift stratigraphic sequences. The acquisition of deep seismic reflection and refraction data has played a key role in helping to understand the structure and rheological layering of the continental lithosphere. This led to the development of more realistic models of continental lithosphere tectonics. The acquisition of deep seismic reflection and refraction data has played a key role in helping to understand the structure and rheological layering of the continental lithosphere. This led to the development of more realistic models of continental lithosphere tectonics. The most up to date models of lithosphere deformation take into account the complex interaction, in 4-dimensions, of structural, thermal, isostatic, rheological, metamorphic and surface processes to simulate the evolution of extensional basins and thrust belt-foreland basin couplets. The most up to date models of lithosphere deformation take into account the complex interaction, in 4-dimensions, of structural, thermal, isostatic, rheological, metamorphic and surface processes to simulate the evolution of extensional basins and thrust belt-foreland basin couplets.

32. Summary - Black Sea and South Caspian Sea case studies It is not possible to reproduce basin subsidence when the magnitude of lithosphere extension is based on the amount of fault controlled deformation. It is not possible to reproduce basin subsidence when the magnitude of lithosphere extension is based on the amount of fault controlled deformation. The large magnitude of Tertiary ("post-rift") subsidence observed in the basins cannot be explained by loading and flexure caused by surrounding thrust belts. The large magnitude of Tertiary ("post-rift") subsidence observed in the basins cannot be explained by loading and flexure caused by surrounding thrust belts. Models in which the magnitude of deformation is constrained using crustal thinning/thickening generate amounts of total subsidence that are comparable with that observed. These models rely upon a depth dependent extension mechanism to reconcile the observed (small) magnitude of faulting with overall attenuation of the crust. Models in which the magnitude of deformation is constrained using crustal thinning/thickening generate amounts of total subsidence that are comparable with that observed. These models rely upon a depth dependent extension mechanism to reconcile the observed (small) magnitude of faulting with overall attenuation of the crust. 3-D modelling of the eastern Black Sea shows that the magnitude of total subsidence is significantly reduced when accounting for a realistic bathymetry, a late stage Upper Miocene - Quaternary infill and regional flexure. The observed subsidence can only be accounted for by the extension of thickened crust or additional subsidence mechanisms (?). 3-D modelling of the eastern Black Sea shows that the magnitude of total subsidence is significantly reduced when accounting for a realistic bathymetry, a late stage Upper Miocene - Quaternary infill and regional flexure. The observed subsidence can only be accounted for by the extension of thickened crust or additional subsidence mechanisms (?).